Method and circuit for controlling or starting a U-shape single phase synchronous permanent magnet motors

ABSTRACT

A method and circuit for controlling or starting a U-shape single phase synchronous permanent magnetic motor (U-SPSPM motor) having a rotor and a stator and coupled to a single phase alternating current (AC) power source through a switch, including estimating back electromotive force (back-EMF) of the motor based on an observer model with inputs indicative of the measured signals, and triggering the switch to supply power to the motor based on the estimates of the back-EMF.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority to and is a continuation of U.S. patentapplication Ser. No. 15/623,512, filed Jun. 15, 2017, now U.S. Pat. No.10,075,110, which is a continuation of U.S. patent application Ser. No.14/969,858, filed Dec. 15, 2015, now U.S. Pat. No. 9,729,093, which areincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

With the development of the advanced motor control technologies in homeappliances, more and more new motor control methods have been proposedto make the home appliance cheaper, more intelligent and smart.Sensorless control is one of the key technologies, which can make motorsrun without a position sensor, such as a Hall sensor, encoder or etc. Itis known to use sensorless control in three phase motor control systems.But three phase motors are not often used in the drains systems of homeappliances such as dishwashers and washing machines. Rather, suchsystems broadly use a U-shape single phase synchronous permanentmagnetic motor (U-SPSPM motor). However, sensorless control of a U-SPSPMmotor is not commonly used for several reasons.

A U-SPSPM motor, without knowing the magnetic rotor position, cannot bestarted in a unidirectional rotation because of cogging torque.Moreover, without rotor position information, any realization of theoptimal power regulation will be impossible. Usually a sensor, such as aHall sensor, is used to get the rotor position information. But thereare several trade-offs with use of a sensor-based control: (1)associated costs for a sensor and wiring, (2) required space to add thesensor and circuitry, and (3) added energy consumption. Thus, there is abenefit to achieving sensorless control of a U-SPSPM motor without aphysical position sensor.

It is known to provide sensorless control of a U-SPSPM motor with only avoltage signal. Only the voltage signal across the motor is used in thismethod to estimate the rotor position. A problem with this method isthat rotor position information is estimable only when the current isequal to zero, i.e., when u=e₀, or when the voltage equals aback-electromotive force. Thus, only detecting motor winding voltagecannot provide a maximum output power and the maximum torque.Consequently, the system will be less efficient based on the same motordesign or motor capability.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, the disclosure relates to a method for controlling aU-shape single phase synchronous permanent magnetic motor (U-SPSPMmotor) having a rotor and a stator and coupled to a single phasealternating current (AC) power source through a switch, the methodincluding measuring a feedback signal representative of voltage acrossthe motor leads, measuring a feedback signal representative of currentthrough the motor, measuring a feedback signal indicative of azero-crossing of the single phase AC power source, estimating backelectromotive force (back-EMF) of the motor based on an observer modelwith inputs indicative of the measured feedback signals, wherein theestimates of the back-EMF has a higher fidelity than the number ofzero-crossings measured, and triggering the switch to supply power tothe motor based on the estimates of the back-EMF.

In another aspect, the disclosure relates to a circuit for controlling aU-shape single phase synchronous permanent magnetic motor (U-SPSPMmotor) including an alternating current (AC) power source connected to aU-SPSPM motor having a rotor, a microcontroller coupled to the AC powersource and to the U-SPSPM motor, a phase sensor connected between the ACpower source and the microcontroller configured to send a signalrepresentative of zero crossing to the microcontroller, a currentsensing circuit coupled to the microcontroller configured to send asignal representative of a current value to the microcontroller, avoltage sensing circuit coupled to the microcontroller configured tosend a signal representative of a voltage value to the microcontroller,a triac connected in series between the AC power source and the U-SPSPMmotor, and coupled to the microcontroller, and an observer model in themicrocontroller configured to determine back electromotive force(back-EMF), wherein the determination of the back-EMF has a higherfidelity than the number of zero-crossings represented by the phasesensor signal.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic, side view of a dishwasher according to a firstembodiment of the invention.

FIG. 2 is a schematic view of a control system of the dishwasher in FIG.1.

FIG. 3 is an enlarged schematic view of a circuit for a sensorlesscontrol in accord with the invention.

FIG. 4 is a flow chart of a method of sensorless speed control using thecontrol circuit of FIG. 3.

FIG. 5 is a flow chart of a starting strategy using the control circuitof FIG. 3.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The invention is generally directed toward sensorless control of aU-SPSPM motor such as those that may be used in a drain system of atreating appliance such as a dishwasher or a washing machine. While thenovelty of the claimed method is not limited to appliances, embodimentsdescribed herein will be in the context of appliances and, morespecifically, to a dishwasher.

FIG. 1 is a schematic, side view of a treating appliance where a U-SPSPMmotor may be used, illustrated here in the context of a dishwasher 10.While the illustrated treating appliance is a dishwasher 10, othertreating appliances are possible, non-limiting examples of which includeother types of dishwashing units, such as in-sink dishwashers, multi-tubdishwashers, or drawer-type dishwashers, washing machines, and otherapplications where a U-SPSPM motor is practical.

The dishwasher 10 may have a cabinet 12 defining an interior, which isaccessible through a door (not shown). The cabinet 12 may comprise achassis or a frame to which panels may be mounted. For built-indishwashers, the outer panels are typically not needed. At least onewash tub 14 is provided within the interior of the cabinet 12 anddefines a treating chamber 16 to receive and treat utensils according toa cycle of operation, often referred to a wash cycle whether or notwashing occurs. The wash tub 14 has an open face that is closed by thedoor.

For purposes of this description, the term “utensil(s)” is intended tobe generic to any item, single or plural, that may be treated in thedishwasher 10, including, without limitation; dishes, plates, pots,bowls, pans, glassware, and silverware.

One or more utensil racks, such as a lower utensil rack 28 and an upperutensil rack 26 may be provided in the treating chamber 16. The racks26, 28 hold utensils (not shown) that may be treated in the treatingchamber 16. The racks 26, 28 may be slid in and out of the treatingchamber 16 through the opening closed by the door.

A liquid supply system is provided for supplying liquid to the treatingchamber 16 as part of a wash cycle for washing any utensils within theracks 26, 28. The liquid supply system includes one or more liquidsprayers, which are illustrated in the form of spray arm assemblies 34,38, 40, that are provided within the treating chamber 16 and areoriented relative to the racks 26, 28 such that liquid sprayed from thespray arm assemblies 34, 38, 40 may be directed into one or more of theracks 26, 28.

It should be noted that the stacked arrangement of the utensil racksmerely serves to illustrate an environment for the invention. Forexample, the invention may be implemented in a stacked arrangementhaving a silverware basket, the lower and upper utensil rack, and withupper, middle, and lower level spray arm assemblies having spray headsfor the silverware basket alternatively arranged in between the lowerand upper utensil rack.

The liquid supply system further comprises a sump 30 to collect bygravity, liquid sprayed within the treating chamber 16. The sump 30 isillustrated as being formed with or affixed to a lower portion of thewash tub 14 to collect liquid that may be supplied into or circulated inthe wash tub 14 during, before, or after a cycle of operation. However,the sump 30 may be remote from the wash tub 14 and fluidly coupled bysuitable fluid conduits.

The liquid supply system further comprises a pump assembly 31 fluidlycoupled to the sump 30, and as illustrated, may include a wash pump 32and a drain pump 33. The wash pump 32 fluidly couples the sump 30 to thespray arm assemblies 34, 38, 40 through a spray arm supply conduit 46 torecirculate liquid that collects in the sump to the spray arm assemblies34, 38, 40 for spraying via the racks 26, 28. The drain pump 33 fluidlycouples the sump 30 to a drain conduit (not shown) for draining liquidcollected in the sump 30 to a household drain, such as a sewer line, orthe like. The wash pump 32 and/or drain pump 33 may be energized by aU-SPSPM motor (not shown explicitly in FIGS. 1 and 2).

While the pump assembly 31 may include the wash pump 332 and the drainpump 33, in an alternative embodiment, the pump assembly 31 may includea single pump, which may be operated to supply liquid to either thedrain conduit or the spray arm support conduit 46 such as by rotating inopposite directions or by valves. In such a case the single pump mayutilize a U-SPSPM motor.

The dishwasher 10 further comprises a control system having variouscomponents and sensors for controlling the flow and condition of theliquid to implement a wash cycle. The control system includes acontroller 50 for implementing one or more cycles of operation. As seenin FIG. 2, the controller 50 is operably coupled to the pumps 32, 33, aheater 46, and one or more sensors 58 to either control these componentsand/or receive their input for use in controlling the components. Thecontroller 50 is also operably coupled to a user interface 56 to receiveinput from a user for the implementation of the wash cycle and providethe user with information regarding the wash cycle. In this way, thecontroller 50 can implement a wash cycle selected by a user according toany options selected by the user and provide related information to theuser.

The controller 50 may also comprise a central processing unit (CPU) 52and an associated memory 54 where various wash cycle and associateddata, such as look-up tables, algorithms, may be stored. Non-limitingexamples of treatment cycles include normal, light/china, heavy/pots andpans, and rinse only. One or more software applications, such as anarrangement of executable commands/instructions may be stored in thememory and executed by the CPU 52 to implement the one or more washcycles. The controller 50 may further include a clock (not shown). Theclock may be alternatively located in another component operably coupledto the controller 50.

The user interface 56 provided on the dishwasher 10 and coupled to thecontroller 50 may include operational controls such as dials, lights,knobs, levers, buttons, switches, and displays enabling the user toinput commands to the controller 50 and receive information about theselected treatment cycle. The user interface 56 may be used to select atreatment cycle to treat a load of utensils. Alternatively, thetreatment cycle may be automatically selected by the controller 50 basedon the soil levels sensed by any sensors in the dishwasher 10 tooptimize the treatment performance of the dishwasher 10 for a particularload of utensils.

Referring to FIG. 3, a circuit 100 may be included at least partially inthe controller 50. The circuit 100 includes a connection to analternating current (AC) power source 102 and a U-SPSPM motor 104. TheAC power source 102 in the United States is typically 120 volts and 60Hz. A microcontroller 106, which may be the CPU 52 or which may be adistinct processor, is coupled to the AC power source by an observercircuit or sensor 108 that detects the zero crossing, i.e., phase, ofthe current flow and sends a ZC signal 109 representative of the phaseof the voltage polarity to the microcontroller 106. The microcontroller106 is also coupled to a current sensing circuit 110 that sends ananalog signal 112 representative of a current value to themicrocontroller. The microcontroller 106 is also coupled to a voltagesensing circuit 114 that senses voltage across the U-SPSPM motor 104 andsends an analog signal 116 representative of a voltage value to themicrocontroller. A triac 118 in series between the (AC) power source 102and the U-SPSPM motor 104 is coupled to the microcontroller 106. Thetriac 118, of course, switches power to the U-SPSPM motor 104 on or off,depending on a trigger signal 120 sent from the microcontroller 106.

The aforementioned structure provides a motor control system forcontrolling the U-SPSPM motor 104 by estimating rotor position withoutthe use of a rotor position sensor. The system estimates the position ofthe rotor of the U-SPSPM motor 104 based on estimates of backelectromotive force (back-EMF). The back-EMF is estimated by an observermodel 122 in the microcontroller 106 based on the analog signal 112 forstator current, the analog signal 116 for stator voltage, and the ZCsignal 109 for the AC zero-crossing (phase). The observer model 122estimates the back-EMF at an arbitrarily fine time resolution to producea high-fidelity back-EMF estimate. Prior art sensorless motorcontrollers only include measuring the back-EMF when the stator currentis zero which limits the fidelity of the back-EMF estimate to thefrequency of the input power source (e.g. a 60 Hz power source has azero-crossing 120 times a second). Because the observer model 122estimates the back-EMF with a high fidelity model, the control systemcan control commutation of the motor on a fine time scale that isindependent of the AC power source. For example, the control system cantrigger the TRIAC 118 based, in part, on the back-EMF estimate.

The back-EMF observer model relates stator current and stator voltage toback-EMF according using the following relationships. Stator windingvoltage is obtained from equation (1):

$\begin{matrix}{u = {{{r_{A}i_{A}} + \frac{d\;\psi_{A}}{dt}} = {{r_{A}i_{A}} + {L_{A}\frac{{di}_{A}}{dt}} + e_{0}}}} & (1)\end{matrix}$

where μ=stator voltage, i_(A)=stator current, r_(A)=stator resistance,and L_(A)=stator inductance. Back-EMF produced by the magnetic rotor isobtained from equation (2):

$\begin{matrix}{e_{0} = {{{- \psi_{0}}\sin\;\theta\;\frac{d\;\theta}{dt}} = {{- \psi_{0}}\omega\;\sin\;\theta}}} & (2)\end{matrix}$

where e₀=back-emf, ψ₀=rotor flux constant, and ω=rotor speed.

Preferably the circuit 100 provides contiguous (if not continuous)estimation of the back-EMF. That is, the voltage and currentmeasurements occur at a sampling rate much higher (and not a functionof) the mains power frequency because the current is directly includedin the back-EMF model (instead of being ignored by only makingmeasurements at the current zero crossing). Therefore, the controlscheme includes estimating the back-EMF at arbitrarily fine resolutioninstead of being defined by the current zero crossing.

Referring now to FIG. 4, a method for controlling the U-SPSPM motor 104commences with a start of a speed control program 130 in themicrocontroller 106. At step 132, the observer circuit or sensor 108detects the zero crossing, i.e., phase, of the current flow and sends aZC signal 109 representative of the phase of the voltage polarity to themicrocontroller 106. At step 134, the voltage sensing circuit 114 sensesvoltage across the U-SPSPM motor 104 and sends an analog signal 116representative of a voltage value to the microcontroller 106. At step136, the current sensing circuit 110 sends an analog signal 112representative of a current value to the microcontroller 106. At step138, the microcontroller 106 operates the observer model 122 to estimatethe back-EMF and the rotor position in the U-SPSPM motor 104. With theknown rotor position from the observer model 122, the microcontroller106 can compare the speed of the rotor with a predetermined synchronousspeed for the U-SPSPM motor 104 at step 140. Based on that comparison,the microcontroller 106 can trigger or adjust the triac 118 to controlthe U-SPSPM motor 104. For example, if the speed is greater than thesynchronous speed, the microcontroller 106 can decrease the triggerangle of the triac 118 at step 142. Conversely, if the speed is notgreater than the synchronous speed, the microcontroller 106 can increasethe trigger angle of the triac 118 at step 144. Either way, with theknown rotor position from the observer model 122, the microcontroller106 can ascertain the rotor polarity at step 146. If the polarity isnorth and the phase voltage is greater than or equal to zero at step148, or if polarity is south and the phase voltage is less than or equalto zero at step 150, the microcontroller 106 can signal the triac 118 onat step 152. Conversely, if the polarity is north and the phase voltageis not greater than or equal to zero at step 148, or if polarity issouth and the phase voltage is not less than or equal to zero at step150, the microcontroller 106 can signal the triac 118 off at step 154.

FIG. 5 illustrates a starting strategy for the U-SPSPM motor 104 usingthe senseless control method of FIG. 4. At startup 200, themicrocontroller 106 enables the triac 118 to allow two pulses to be sentto the U-SPSPM motor 104 at step 202. Meanwhile the observer model 122estimates the back-EMF and the rotor position in the U-SPSPM motor 104at step 204, and the microcontroller 106 determines whether anintegration of the back-EMF exceeds a predetermined threshold. If theintegration is less than the threshold, the microcontroller 106initiates a start sequence for the U-SPSPM motor 104 for one polarity atstep 206. If the integration is more than the threshold, themicrocontroller 106 initiates a different start sequence for the U-SPSPMmotor 104 for the other polarity at step 208. Based on the analogsignals 112, 116, the microcontroller 106 can determine if the motor hasstarted at step 210. If NO, then the associated pump (wash or drain forexample) is off, and the method reverts to the startup 200. If YES, thenthe microcontroller 106 can compare the speed of the rotor with apredetermined synchronous speed for the U-SPSPM motor 104 at step 212.If NO, then the microcontroller 106 can adjust the triac 118 at step 214as above to achieve synchronicity, and if not then, the associated pumpwill remain off. If synchronicity is achieved, then the associated pumpwill be ON and working normally at step 216.

While the invention has been specifically described in connection withcertain specific embodiments thereof, it is to be understood that thisis by way of illustration and not of limitation. Reasonable variationand modification are possible within the scope of the forgoingdisclosure and drawings without departing from the spirit of theinvention which is defined in the appended claims.

What is claimed is:
 1. A method for controlling a U-shape single phasesynchronous permanent magnetic motor (U-SPSPM motor) having a rotor anda stator and coupled to a single phase alternating current (AC) powersource through a switch, the method comprising: measuring a feedbacksignal representative of voltage across the motor leads; measuring afeedback signal representative of current through the motor; measuring afeedback signal indicative of a zero-crossing of the single phase ACpower source; estimating back electromotive force (back-EMF) of themotor based on an observer model with inputs indicative of the measuredfeedback signals, wherein the estimates of the back-EMF has a higherfidelity than the number of zero-crossings measured; and triggering theswitch to supply power to the motor based on the estimates of theback-EMF.
 2. The method of claim 1 wherein estimating back-EMF includescontinuously estimating back-EMF.
 3. The method of claim 1 whereinestimating back-EMF includes estimating back-EMF more than 120 times persecond.
 4. The method of claim 1 wherein estimating back-EMF occurs at atime scale independent of the single phase AC power source frequency. 5.The method of claim 1 further comprising estimating a rotational speedof the motor and a position of the rotor based on the estimates of theback-EMF.
 6. The method of claim 5 wherein triggering the switch tosupply power to the motor is further based on the estimates of therotation speed of the motor and the position of the rotor.
 7. The methodof claim 1 wherein the feedback signal representative of the voltageacross the U-SPSPM motor leads is measured by a voltage sensing circuitcoupled to a microcontroller, and configured to send the feedback signalto the microcontroller.
 8. The method of claim 1 wherein the feedbacksignal representative of the current through the U-SPSPM motor ismeasured by a current sensing circuit coupled to a microcontroller, andconfigured to send the feedback signal to the microcontroller.
 9. Themethod of claim 1 wherein the feedback signal indicative of azero-crossing of the single phase AC power source is measured by a phasesensor connected between the AC power source a microcontroller, andconfigured to send the feedback signal to the microcontroller.
 10. Themethod of claim 1 wherein the switch is a triac and further comprisingadjusting a trigger angle of the triac based on at least one of theback-EMF and a rotational speed of the motor and a position of therotor.
 11. The method of claim 1 further comprising comparing the speedof the rotor with a predetermined synchronous speed for the U-SPSPMmotor.
 12. The method of claim 11 further comprising adjusting theswitch if the speed of the rotor is greater than or less than thesynchronous speed.
 13. The method of claim 12 wherein adjusting theswitch includes decreasing a trigger angle of a triac.
 14. The method ofclaim 12 wherein adjusting the switch includes increasing a triggerangle of a triac.
 15. The method of claim 1 wherein the triggeringincludes setting the switch ON when polarity of the rotor is north andthe phase value is greater than or equal to zero, or if polarity issouth and the phase value is less than or equal to zero.
 16. The methodof claim 1 wherein the triggering includes setting the switch OFF whenpolarity of the rotor is north and the phase value is not greater thanor equal to zero, or if polarity is south and the phase value is notless than or equal to zero.
 17. A circuit for controlling a U-shapesingle phase synchronous permanent magnetic motor (U-SPSPM motor)comprising: an alternating current (AC) power source connected to aU-SPSPM motor having a rotor; a microcontroller coupled to the AC powersource and to the U-SPSPM motor; a phase sensor connected between the ACpower source and the microcontroller configured to send a signalrepresentative of zero crossing to the microcontroller; a currentsensing circuit coupled to the microcontroller configured to send asignal representative of a current value to the microcontroller; avoltage sensing circuit coupled to the microcontroller configured tosend a signal representative of a voltage value to the microcontroller;a triac connected in series between the AC power source and the U-SPSPMmotor, and coupled to the microcontroller; and an observer model in themicrocontroller configured to determine back electromotive force(back-EMF), wherein the determination of the back-EMF has a higherfidelity than the number of zero-crossings represented by the phasesensor signal.
 18. The circuit of claim 17 in a dishwasher where theU-SPSPM motor is associated with one of a wash pump or a drain pump.